A system, for example, a microwave communication system, that requires an extremely small gain step (Step) of a variable gain amplifier (Variable Gain Amplifier, VGA for short), also has high requirements on linearity and noise, and it is costly to implement the requirements by using a programmable gain amplifier (Programmable Gain Amplifier, PGA for short) solution. Therefore, it is usually expected that a gain continuously change with a control voltage. That is, the requirements are implemented by using a continuous variable gain amplifier (Continuous VGA).
For continuous variable gain amplifiers in the prior art, some do not provide ideal linearity, and some cause a noise figure (Noise Figure, NF for short) to seriously deteriorate with attenuation of the gain.